T. H. Holland — Gonstitution of Later ite. 63 



of lower levels is not, however, developed at this elevation, which 

 accounts for the restrictive remark in the Manual of the Geology of 

 India ^ ; and it is likely that the high temperature assists the 

 <5oncretionary structure in the way indicated in the sequel. Pre- 

 paratory to the suggestion offered below it should be premised that 

 the climate of the Nilgiri and Palni highlands differs from "that of 

 the temperate zone in the absence of a real winter : in the fact 

 that very low temperatures do not occur ; so a winter temperature, 

 maintained for a long period, may be fatal to pronounced lateritic 

 development, and may possibly prevent its formation altogether 

 in high latitudes, where, as we know, fresh felspars are preserved 

 in detrital materials. 



On the other hand, when vapours (or liquids) from deep-seated 

 sources act on aluminous silicates, presumably at high temperatures, 

 hydrous silicate of alumina, kaolin, is formed, and not, so far as 

 recorded, the simple hydrous oxides. 



Now, putting these facts together, I would suggest that we look 

 for the explanation of laterite, not in simple chemical reactions, but 

 in the action of some lowly organism having the power of separating 

 the alumina, which, after the manner of many plants, it does not 

 want, from the silica, which is necessary for its life, but which, 

 being in a soluble form, is removed again by the alkaline solutions. 

 Such a form of life might thrive in the moist climate of the tropics, 

 even to a temperate altitude, but might find life intolerable in 

 a land subject to severe winters, such as we get in the temperate 

 zone and in North India, where we find no laterite. Such an 

 organism would form Tcunkar as well as laterite in a moist, warm 

 climate, the difference in the products being due merely to their 

 after-treatment by water. For obvious reasons, too, such an organism 

 could not live under conditions of kaolinization. But apart from 

 the agency of life I see no chemical reason why an aluminous 

 silicate should undergo a more complete decomposition at the 

 comparatively low temperature of the tropics than at the high 

 temperature of subterranean situations ; the contrary, indeed, seems 

 more natural. And if the temperature does so affect chemical action, 

 we still might wonder why laterite does not occur on the foot-hills 

 of the Himalayas, where there is an abundance of moisture and 

 where the average annual temperature is as high as on the Nilgiris. 

 Chemical changes which cease at low temperatures commence again 

 as soon as the suitable physical conditions are restored, and laterite, 

 consequently, would be expected to form in North India during the 

 summer. But the distribution of an organism might very well be 

 limited by the extremes of climate, when possibly the average 

 annual temperature is not below what would be congenial to it if 

 maintained. 



If this fancy turns out to be well founded we must add 

 lateritization to the long list of tropical diseases, against which 

 even the very rocks are not safe. But it is a big step between the 

 -establishment of a reasonable suspicion and the actual detection of the 



1 2nd ed., 1893, p. 375. 



